Method for shortening a cable probe

ABSTRACT

A method for shortening a cable, which is mounted in a device housing of a measurement device, of a cable probe, comprising the step of: removing the measurement device electronics; interrupting the electrical connections between the measurement device electronics and the cable probe; releasing a built-in sleeve which surrounds the cable, as a result of which at least one seal which surrounds the cable and acts with respect to a medium to be measured, is relieved of load; drawing out of the device housing the built-in sleeve, together with the cable and the seal; shortening the cable by a desired length; once again drawing over the remaining cable of the cable probe, a seal, a built-in sleeve and clamping cone and mounting the cable in the built-in sleeve, by pulling it into said built-in sleeve; once again making the electrical connections between the cable probe and the measurement device electronics; and once again closing the device housing once the measurement device electronics have been fitted.

This is a divisional of application Ser. No. 09/749,747, filed Dec. 28,2000, now U.S. Pat. No. 6,414,242.

FIELD OF THE INVENTION

The invention relates to a measurement device having a cable probe, andto a method for shortening the cable of a cable probe.

BACKGROUND OF THE INVENTION

Various embodiments of measurement devices having cable probes areknown, which normally comprise a housing in which measurement deviceelectronics are accommodated, and to which a probe is fitted which is inthe form of a cable, a bar or rod. For example, a capacitive measurementdevice is known from level measurement, in which at least one electrode(which is used for measurement) of the measurement capacitor is in theform of a cable or rod which is immersed in the medium to be measured.In a further measurement device for level measurement, electromagneticpulses, for example, are transmitted on a waveguide, which is in theform of a rod or cable and is immersed in the medium to be measured, tothe surface of the medium. A hydrostatic measurement device is also usedfor level measurement, in which a pressure sensor is mounted at the endof a cable and is lowered into the medium to be measured. All theseprobes which are in the form of cables, bars or rods and are connectedto a measurement device, are referred to for the sake of simplicity, inthe following text by the term “cable probes”. The bars, rods or cablesare accordingly referred to, for the sake of simplicity, as “cables”.

The measurement devices having cable probes are normally mounted on acontainer which contains the medium to be measured, with the housingfrequently being mounted in or on a container wall such that the cableprobe projects into the interior of the container, and into the medium.The cable probes are either themselves electrically conductive, or haveat least one electrical conductor in the interior, in the sense ofelectrical wires. The cables or the electrical conductors are normallyconnected to measurement device electronics in which the measurementsignals are produced and processed. The measurement device electronicsare in turn normally connected to an instrument or switching console orto some other higher-level unit, where the level measurements areprocessed.

A common feature of all these cable probes is that their length dependson the medium level expected or to be measured. If the cable probe needsto be shortened in response to changed measurement conditions, then,normally, the shortening of the cable and its processing, in particularits mounting, are problematic and difficult to carry out. A special toolis often required for this purpose, so that, in many cases, the work canbe carried out only at the manufacturer's premises or supplier of themeasurement device. Furthermore, with various devices, the electricalconnection of the cable probe to the measurement device electronics islinked to the mechanical mounting of the cable in such a way that thecable probe cannot be shortened in a simple manner.

SUMMERY OF THE INVENTION

One object of the invention is thus to provide a measurement devicehaving a cable probe, and a method according to which the cable probecan be shortened in a simple manner by an end user, to be precise ifpossible on site and without needing to use any special tools or othermanufacturer-specific tools.

This object is achieved according to the invention by a measurementdevice

having a device housing which accommodates measurement deviceelectronics,

having a cable probe mounted therein,

which comprises a built-in sleeve provided in the interior of the devicehousing,

which built-in sleeve can be fitted in or removed from the interior ofthe device housing by rotation about its longitudinal axis

and whose operating position is fixed by at least one detachablemounting.

One advantageous embodiment of the invention provides that the cableprobe comprises a cable which is mounted in the built-in sleeve by meansof a clamping cone which surrounds the cable.

In a further advantageous embodiment, the built-in sleeve is surroundedby a connecting sleeve of the device housing.

In another particularly advantageous embodiment of the measurementdevice according to the invention, the built-in housing has a mountingcollar by means of which the built-in sleeve is mounted in its operatingposition in the device housing by means of a number of screws.

Even further embodiments of the invention provide that electricalconductors, which are located in the interior of the cable of the cableprobe and are passed out in the built-in sleeve, are connected to a plugand/or to a plug connecting socket, in which the plug or the plug socketcan be accommodated by the built-in sleeve.

Further advantageous embodiments of the measurement device according tothe invention relate to a seal in an internal area of the connectingsleeve from a medium to be measured by means of a conical seal which islocated in the interior of the connecting sleeve and surrounds thecable.

In other special embodiments of the invention, further seals are used inorder to seal a part of the device housing which accommodates themeasurement device electronics from an internal area of the connectingsleeve which accommodates the cable probe, and/or from an internal areaof the built-in sleeve.

Furthermore, the invention achieves the object by means of a method forshortening a cable, which is mounted in a device housing of ameasurement device, of a cable probe, comprising the following methodsteps:

a) after opening the device housing, the measurement device electronicsare removed;

b) electrical connections between the measurement device electronics andthe cable probe are interrupted;

c) releasing a built-in sleeve mounted on the housing side, whichbuilt-in sleeve surrounds the cable as a result of which at least oneseal which surrounds the cable and acts with respect to the medium to bemeasured, is relieved of load in a connecting sleeve which alsosurrounds the cable of the cable probe;

d) the built-in sleeve is drawn out of the device housing, together withthe cable and the seal;

e) the cable is shortened by a desired length;

f) a seal, a built-in sleeve and clamping cone are once again drawn overthe remaining cable of the cable probe, and the cable is mounted in thebuilt-in sleeve, by pulling it into said built-in sleeve;

g) the electrical connections between the cable probe and themeasurement device electronics are made once again;

h) once the measurement device electronics have been fitted, the devicehousing is closed once again.

One particular advantage of the invention is that the only tools whichare required to shorten the cable probe are a conventional screwdriver,pliers for cutting through and cutting off the cable of the cable probe,and/or a cutting tool like to a blade for exposing the electricalconductors contained therein.

A further advantage of the invention is that the cable of the cableprobe can be shortened without the housing of the measurement deviceneeding to be removed from a container which contains the medium to bemeasured.

The invention will be described and explained in the following textusing an exemplary embodiment and with reference to the attacheddrawing. Identical features and parts of the various embodiments of theinvention are provided with the same reference symbols, for simplicity.In the figures:

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows an exemplary embodiment of a measurement device having acable probe according to the invention with an essentially cut-openhousing, showing a longitudinal section with details in the interior ofthe housing;

FIG. 2 shows the measurement device having the cable probe as shown inFIG. 1, in a longitudinal section rotated through 90° about alongitudinal axis in comparison to FIG. 1;

FIG. 3 shows a detail X of the measurement device shown in FIG. 1,corresponding to the marking there;

FIG. 4 shows a perspective view of the cable probe of the measurementdevice shown in FIG. 1, with the individual parts shown in an explodedview;

FIG. 5 shows a detail Z of the measurement device shown in FIG. 4,corresponding to the marking there;

FIG. 6 shows a perspective view of the individual parts of themeasurement device shown in FIG. 1;

FIG. 7 shows a perspective view of the interior of the housing of themeasurement device shown in FIG. 1, after the cable probe has beenfitted;

FIG. 8 shows a perspective front view of the measurement deviceelectronics; and

FIG. 9 shows a perspective view of the measurement device electronicsshown in FIG. 9, from underneath.

DETAILED DESCRIPTION OF PREFERRED AND ALTERNATIVE EMBODIMENTS

FIGS. 1 and 2 show a first exemplary embodiment of a measurement device10 having a cable probe 40 according to the invention. The illustratedmeasurement device 10 may be, for example, a level measurement devicewhich is known per se and is mounted on a container (which is notillustrated here) in such a way that the cable probe (40) is immersed ina medium whose level in the container is intended to be measured. Levelmeasurement devices of the type illustrated here include, for example,those which allow the level to be determined capacitively or bymeasuring the hydrostatic pressure of the medium in the container bymeans of a differential pressure sensor, which is arranged at the end ofthe cable probe 40 but is not illustrated here. However, it is alsofeasible for the invention to be used with other measurement devices, inwhich the level is determined by means of electromechanical signalscarried on the cable probe.

The measurement signals are converted by measurement device electronics12, accommodated in the measurement device 10, into signals whichcorrespond to the level, and are passed to a process control unit, forexample an instrument console, which is not illustrated here. It is alsofeasible for the signals which correspond to the level to be carried ona data bus, which is not illustrated here but is connected to such aprocess control unit. Although the invention will be explained in thefollowing text with reference to exemplary embodiments from levelmeasurement, any type of measurement devices with cable probes isfeasible for the invention.

An electronics housing, denoted by 14, which surrounds the measurementdevice electronics 12, is accommodated in a device housing 22 (which isillustrated partially cut open) of the measurement device 10, to be moreprecise in a housing pot 24. The housing pot 24 is closed by a cover 26.The housing pot 24 has a connecting sleeve 28 arranged on it, whicheither forms an integral unit with the housing pot 24 or, as shown inFIGS. 1 and 2, is mounted on the housing pot 24, for example by means ofscrews 30, which mount the connecting sleeve 28 on a mounting apparatus32 provided in the housing pot 24.

The connecting sleeve 28 has a central opening 34 which accommodates abuilt-in sleeve 42, in whose central opening 50 a cable 44 of the cableprobe 40 is mounted. The built-in sleeve 42 for this purpose preferablycomprises a virtually cylindrical part 46 and a conical part 48, withthe cable 44 being mounted in the continuous central opening 50 by meansof a clamping cone 52, by being clamped in a self-retaining manner in anappropriately designed conical region of the central opening 50 of thebuilt-in sleeve 42, as is shown in FIGS. 1 and 2. A lower part 36 of theconnecting sleeve 28 merges into a tip 38, with the unobstructedinternal diameter of its central opening 34 being reduced continuouslydown to approximately the external diameter of the cable 44 in thisregion, to be more precise in the interior of the tip 38. A sealing cone54, preferably composed of elastomer material, is provided here,surrounds the cable 44 forming a seal, and also seals the interior ofthe connecting sleeve 28, that is to say its central opening 34.Furthermore, as shown in FIGS. 1 and 2, a plate-spring gland 56 isprovided in the interior of the connecting sleeve 28, between thebuilt-in sleeve 42 and the sealing cone 54, and is supported on one sideon the sealing cone 54 while on the other side, as will be explainedlater, allowing a removal of the built-in sleeve 42.

A mounting collar 62 is fitted on that end of the built-in sleeve 42which, as illustrated in FIGS. 1 and 2, projects beyond the connectingsleeve 28 into the housing pot 24, and this mounting collar 62 projectsoutward beyond the virtually cylindrical part 46 of the built-in sleeve42. The built-in sleeve 42, and thus the cable probe 40, are held andfixed in their operating position by means of screws 66, which arepassed through screw bushings 64 in the mounting collar 62 and areanchored in the mounting apparatus 32 in the device housing 22. Thescrews 66 are, for example, conventional slot-headed screws, preferablywith a cruciform-slotted head, as illustrated in FIG. 7.

Furthermore, FIGS. 1 and 2 illustrate electrical conductors 70 of thecable probe 40, which are arranged in the interior of the cable 44.These electrical conductors 70 are exposed above the clamping cone 52and are electrically connected in a desired manner to a plug connectingsocket 72. The plug connecting socket 72 is accommodated in a pluginsert 74, which is accommodated by the central opening 50 of thebuilt-in sleeve 42 and is held in the region of the mounting apparatus32. Suitable plug pins 18 are fitted on the electronics housing 14 andare surrounded by a plug container 16. When the measurement deviceelectronics 12 are being fitted in the housing pot 24, the plug pins 18are inserted into the plug connecting socket 72, thus producing anelectrical connection between the electrical conductors 70 and themeasurement device electronics 12. Suitable guides are provided forcorrect positioning of the plug pins 18 on the plug container 16 and onthe plug connecting socket 72, and these allow the plug pins 18 to belocated only in a desired and preferred position.

Since the illustration chosen in FIG. 2 shows a longitudinal sectionrotated through 90° about the longitudinal axis from the illustration inFIG. 1, FIG. 2 shows two fastening screws 80 in addition to those shownin FIG. 1, by means of which the electronics housing 14, and thus themeasurement device electronics 12, is mounted in its position in thehousing pot. The fastening screws 80 are preferably of the samecommercially available type as the screws 66, for example screws with acruciform-slotted head. For completeness, FIGS. 1 and 2 also show cablebushings 82, through which cables are passed out of the device housing22, in order to connect the measurement device electronics 12 to theinstrument console.

FIG. 3 shows a detail X from FIG. 1. As a special configuration of themeasurement device 10, this figure illustrates a first elastomer seal20, which seals an intermediate area between the plug container 16 ofthe electronics housing 14 and the mounting collar 62 of the built-insleeve 42. This first elastomer seal 20 can be fitted on to anappropriate sealing seat in the built-in sleeve 42. The first elastomerseal 20 is, however, preferably fitted to the plug container 16, as isillustrated in FIGS. 8 and 9. In this case, for the sake of simplicity,it can be sprayed on. Together with second elastomer seal 84, which isprovided on the conical part 48 of the built-in sleeve 42 and isillustrated in FIGS. 1 and 2, the first elastomer seal 20 ensures thatthe measurement device 10—for the theoretical situation where the cable44 is torn off during operation—satisfies even the most stringentpossible requirements with regard to absolute sealing from the medium,and any other influences from the container. The two elastomer sealsensure that the housing pot 24 which accommodates the measurement deviceelectronics 12 is in all situations sealed both from the internal area,that is to say from the central opening 34 of the connecting sleeve 28,and from the internal area, that is to say from the central opening 50of the built-in sleeve 42. It is evident that the elastomer seals 20 and84 are used only in those situations where a licensing authority placesrelatively stringent requirements on sealing from the medium. In mostconventional applications, the seals 20 and 84 are thus not required.

FIG. 4 shows the cable probe 40 in the removed state and without thesurrounding connecting sleeve 28. This clearly shows how the sealingcone 54 surrounds the cable 44 forming a seal. The plate-spring gland 56is pushed over the cable 44 between the sealing cone 54 and the built-insleeve 42, and its layers are shown in more detail in FIG. 5. It isevident from this that the individual plate springs are as far aspossible arranged on one another in opposite senses in order that theyallow the greatest possible travel when relieved of load. A plate spring58, which is referred to here as the “topmost” corresponding to thechosen illustration, and a plate spring 60 which is accordingly referredto as the “bottom most”, are each arranged with their broad contactsurface facing the built-in sleeve 42 and the sealing cone 54,respectively.

FIG. 4 also shows the construction of the mounting collar 62 of thebuilt-in sleeve 42. The screw bushings 64, preferably three, are in theform of elongated holes and allow the fastening screws 66 to be passedthrough, or allow the mounting collar 62 to be placed over screws 66which have already been fastened in the device housing 22 (in thiscontext, see FIG. 1, 2 or 7). The screw bushings 64 preferably eachinternally have contact surfaces 86 against which the screw heads canrest in order thus to secure the built-in sleeve 42 when the screws 66are tightened, as illustrated in FIG. 7. For this purpose, as mentioned,the mounting collar 62 is normally placed over the screws 66 and isrotated about the central longitudinal axis of the built-in sleeve 42.In a similar way to the so-called bayonet fitting, the screws 66 areguided in the screw bushings 64 and limit the rotary movement. Once thescrews 66 have reached the desired position with respect to the cutsurfaces 86 (see FIG. 7) they are tightened.

The clamping cone 52 shown in FIG. 4 is arranged above the built-insleeve 42 on the cable 44. The electrical conductors 70 of the cable 44can likewise be seen, and have had the insulation which surrounds themremoved above the clamping cone 52 so that they open into the plugconnecting socket 72, where they are connected to the respectivelydesired connecting contacts.

By pulling the cable 44 in the direction indicated by an arrow 88, it ispulled with the clamping cone 52 into the built-in sleeve 42, and isfirmly clamped there. Any gap between the clamping cone 52 and the plugconnecting socket 72 has in this case been selected such that the plugconnecting socket 72 and the plug insert 74 surrounding it areaccommodated by the built-in sleeve 42, as already shown in FIGS. 1 and2, in which case a certain length in the form of safety loops should beprovided for the electrical conductors 70. Once the clamping cone 52 hasbeen pulled (with the cable 44) into the built-in sleeve 42, theplate-spring gland 56 is pushed together with the sealing cone 54against the built-in sleeve 42, forming a seal, as in shown in FIG. 6.However, this procedure is not necessary in every case. Normally, it maybe sufficient to pull on the cable 44 outside the connecting sleeve 28,in order in this way to pull the sealing cone 54, the plate-spring gland56 and the built-in sleeve 42, together with the clamping cone 52clamped in it, into the connecting sleeve 28.

Together with the plug connecting socket 72 in the plug insert 74, thecable 44 located in the built-in sleeve 42 and secured by means of theclamping cone 52, and together with a sensor mounted thereon, notillustrated here, the built-in sleeve 42 forms the unit which isreferred to above as the cable probe 40. In a view into the interior ofthe housing pot 24 of the device housing 22, FIG. 7 shows the cableprobe 40 mounted there, once the cable probe 40, to be more precise itsbuilt-in sleeve 42, has been pulled into the housing pot 24 and theconnecting sleeve 28, and has been secured in the desired position thereby means of the screws 66.

Once the measurement device electronics 12 in the electronics housing 14have been fitted into the housing pot 24 and onto the mounting collar 64such that the plug pins 18 on the electronics housing 14 engage in theplug connecting socket 72, the electronics housing 14 is secured in itsposition in the housing pot 24 by means of the screws 80 (in thiscontext, see also FIG. 2). Once the connecting cables 90 have beenpassed through the cable bushings 82 to the instrument console, thedevice housing 22 is closed by the cover 26 illustrated in FIG. 6. Asalready described above, this situation is illustrated in FIGS. 1 and 2.

FIGS. 8 and 9 once again show the electronics housing 14, whichaccommodates the measurement device electronics 12. The plug container16 which surrounds the plug pins 18 is shown here. This plug container16 on the one hand protects the plug pins 18, and on the other hand, byvirtue of its special shape with a type of guide tab, ensures that itand thus the electronics housing 14 can be fitted onto the built-insleeve 42 in only one, desired, correct position. Said guide tab forthis purpose engages in a corresponding recess in the plug insert 74 (inthis context, see FIGS. 4 and 7), thus ensuring that this is the onlyway in which the electronics housing 40 can be accommodated completelyby the housing pot 24, and that the latter can be closed by the cover 26(in this context, see FIGS. 1 and 2).

This also clearly shows the already mentioned first elastomer seal 20,which is provided in the bottom of the plug container 16 on theelectronics housing 14 and allows the measurement device 10 having thecable probe 40 according to the invention to satisfy even relativelystringent requirements for sealing. In their base on the electronicshousing 14, the plug pins 18 are preferably also extrusion coated with athin layer of elastomer material, so that the point where they passthrough the electronics housing 14 is also reliably sealed. Forsimplicity, the connecting cables 90 are only indicated in FIGS. 8 and9.

So far, the advantageous construction and assembly of the measurementdevice 10 with the cable probe 40 according to the invention has beenexplained. One particular advantage of the invention is, however, thatit allows the cable 44 to be shortened in a simple way. Once the cover26 has been loosened and removed from the device housing 22, theconnecting cables 90 are released, and the fastening screws 80 arecompletely released by means of a conventional screwdriver. Themeasurement device electronics 12 which are accommodated in theelectronics housing 14 are then pulled off the built-in sleeve 42, andthe plug connection to the plug connecting socket 72 of the cable probe40 is disconnected. Once the measurement device electronics 12 have beenremoved from the device housing 22, this results in the view illustratedin FIG. 7. There is no need to remove or disassemble the measurementdevice 10 from a container on which it is mounted.

Loosening the screws 66 results in the load on the plate-spring gland56, which is subject to spring stress, being relieved, and the built-insleeve 42 is pushed out of its previous seat. The special shape of thescrew bushings 64 with the contacts 86 (in this context see FIG. 7)limits the travel of the built-in sleeve 42. Further loosening of thescrews 66, but without having to remove them completely from their seat,allows slight rotation of the built-in sleeve 42, and thus of the cableprobe 40, about its longitudinal axis, to be precise to such an extentthat the cable probe 40 can be raised above the screws 66 and can bepulled out of the device housing 22, as is illustrated in FIG. 6.

There are now two possible ways to shorten the cable 44. The built-insleeve 42, the clamping cone 52 as well as the plate-spring gland 56 andthe sealing cone 54 may or may not be reused.

In the second case, which is that which will probably occur morefrequently in practice, the cable probe 40 is pulled out of the devicehousing 22 by somewhat more than the desired shortening length, and thecable is cut through as appropriate, preferably using a conventionaltool. Then, and after removing the previous built-in sleeve 42 and theprevious sealing cone 54, a new sealing cone 54, a new plate-springgland 56, a new built-in sleeve 42 and a new clamping cone 52 are pushedover the shortened cable 44. The electrical conductors 70 of the cable44 are exposed, their insulation is removed, and they are connected to anew plug connecting socket 72, as is shown in FIG. 4. If a mesh of steelwires is used for reinforcement or shielding in the cable 44, then it isself-evident that this mesh must likewise be correspondingly shortened.Once a new plug insert 74 has been fitted onto the plug connectingsocket 72, the clamping cone 42, together with the plate-spring gland 56and the sealing cone 54, is pulled into the device housing 22 onceagain, and the built-in sleeve is pushed over the screws 66. After aslight rotary movement, the screws 66 can be tightened, and themeasurement device electronics 12 can be fitted. Once the electronicshousing has been mounted in the desired position and the connectingcables 90 have been connected, the device housing 22 can be closed bythe cover 26 once again and, in principle, is ready for renewedoperation.

As is provided in the first case, mentioned above, for shortening thecable 44, the sealing cone 54, the plate-spring gland 56, the built-insleeve 42, the clamping cone 52 as well as the plug connecting socket 72and the plug insert 74 can also, of course, be reused. In each of thetwo described cases, the invention allows the cable 44 of the cableprobe 40 to be shortened in a simple manner, to be precise in the field,and by using a normal tool which people there carry with them daily.

What is claimed is:
 1. A method for shortening a cable, which is mountedin a device housing of a measurement device, of a cable probe,comprising the steps of: a) removing the measurement device electronicsafter opening the device housing; b) interrupting the electricalconnections between the measurement device electronics and the cableprobe; c) releasing a built-in sleeve which surrounds the cable, as aresult of which at least one seal which surrounds the cable and actswith respect to a medium to be measured, is relieved of load; d) drawingout of the device housing the built-in sleeve, together with the cableand the seal; e) shortening the cable by a desired length; f) once againdrawing over the remaining cable of the cable probe, a seal, a built-insleeve and clamping cone and mounting the cable in the built-in sleeve,by pulling it into said built-in sleeve; g) once again making theelectrical connections between the cable probe and the measurementdevice electronics; and h) once again closing the device housing oncethe measurement device electronics have been fitted.